1. Field of the Invention
This invention relates to a photoelectric conversion apparatus having an electric charge storage area, the electric potential of which is controlled via a capacitor.
2. Related Background Art
FIG. 1A is a schematic plan view of one example of a photoelectric conversion apparatus disclosed in Laid-Open European Application No. 132076. FIG. 1B is a cross-sectional view taken along the line A--A' of FIG. 1A. FIG. 1C is an equivalent circuit diagram of the apparatus.
In FIGS. 1A and 1B, photoelectric conversion cells are arranged on an n-silicon substrate 101 in which each cell is electrically isolated from adjacent cells by a cell separation area 102 of SiO.sub.2, Si.sub.3 N.sub.4 or polysilicon or the like.
Each cell has the following structure: p-areas 104 and 105 are formed by doping p-type impurities, for example, of boron into an n.sup.- -area 103 of low impurity density formed using epitaxial techniques, or the like, and an n.sup.+ -area 106 is formed in p-area 104 using impurity diffusion techniques, ion implantation techniques or the like.
The p-areas 104 and 105 are a source and a drain area of a p-channel MOS transistor while p-areas 104 and n.sup.+ -106 are a base and an emitter, respectively, of an npn-bipolar transistor. The p-area 104 is both the source of the p-channel MOS transistor and the base of an npn-bipolar transistor.
Formed on n.sup.- -area 103, on which the respective areas are thus formed, is an oxide film 107 on which are formed the gate electrode 108 of a p-channel MOS transistor and a capacitor electrode 109 having a predetermined area. Capacitor electrode 109 opposes p-area 104 with oxide film 107 formed therebetween to form a capacitor.
In addition, an emitter electrode 110 connected to n.sup.+ -area 106, an electrode 111 connected to p-area 105 and a collector electrode 112 on the back of substrate 101 with an ohmic contact area disposed therebetween are formed.
The basic operation of this device will now be described. Assume first that the p-area 104 which is the base of the bipolar transistor is at an initial negative potential. Light enters p-area 104 to produce electron-positive hole pairs, the positive holes of which are stored in p-area 104 to raise the potential of p-area 104 in the positive direction.